There is a considerable interest in radiating ultra-short broadband pulses in mm-wave and THz regime for applications in 3D imaging, spectroscopy, ranging, chemical sensing, precision time transfer, precision frequency transfer, and high-speed wireless communication that may have applicability to a wide variety of technology areas, such as oil and gas, medical, gaming, etc. Unfortunately, the pulse width of the prior silicon-based radiators is not short enough and their bandwidth is limited.
The oil and gas industry uses various logging tools to measure formation properties such as porosity, fluid saturation, fluid type, and permeability. Furthermore, they are used for geo-steering in horizontal drilling and fracture detection. The sensors should provide high vertical and azimuth resolutions. FIG. 1 summarizes the performance of existing logging tools. Although conventional high-resolution tools such as micro-resistivity sensor provide resolution of few cm, they are not suitable for operation with oil-based mud. The resistivity measurement requires passing electric current through a conductive borehole fluid, which cannot be done with oil-based mud. By increasing the frequency, it is possible to perform capacitive logging. Although capacitive probing is possible in oil-based mud, it is very difficult to calibrate the tool and measure the complex permittivity of the formation with high accuracy. A capacitive probe measures the combined permittivity of the mud, mudcake, and the actual formation. Since the permittivity and thickness of mud and mud-cake vary, a precise calibration becomes very challenging.
A radar imaging system and method discussed herein may provide high-resolution imaging. The system may provide solid-state impulse radar sensors in the frequency range from 1 GHz to 1 THz. The radar sensor may radiate ultra-short impulses with duration of 50 psec or less to the formation and measure the reflected signal. Further, the radar sensor does not require a continuous wave oscillator to provide narrow pulses. The radiated pulse can penetrate through the high-resistivity oil-based mud and image the formation behind the mud. Since the radar sensor is not a contact-based probe, it can provide high-resolution images in nonconductive oil-based mud. The radar sensor may provide vertical resolution of 10 mm or better, azimuth resolution of 5° or better, and investigation depth of 10 cm or better.
The radar sensor can also be used to image the cross section of oil pipelines. The pipeline images provide useful information about the geometry of the pipeline, deposition thickness of asphaltenes and wax, velocity of the fluid, as well as size, type, and concentration of gas bubbles, water, or solid particles in the flow.